Well I voted for most of the dragons, except blue (rarely use deserts). I had a world where "the only good dragon is one that doesn't want anything you have." Which had gold, copper, brass and bronze dragons, none of which could shapechange.
White dragons have been the most common. A simlacrum of an old (previously slain) white will show up in the next session or two.
I have also used emerald, magma and shadow dragons